This invention relates to DNA coding for a signal peptide which acts to secrete proteins out of cells and to a DNA containing said signal peptide.
The signal peptide herein means a peptide acting so that proteins formed in cells can be secreted out of the cells. Generally, proteins are produced in cells and accumulated therein. On the other hand, those proteins having a signal peptide are said to be secreted out of cells along with their formation therein. Accordingly, proteins formed in cells can be successfully secreted out of the cells if such a signal peptide is utilized.
Secretion of proteins out of cells could have the following advantages: Firstly, if proteins formed in cells can be moved out of the cells, it will become possible to readily separate contaminatings from the proteins, which reduces the labor required for the purification and isolation thereof. In addition, the proteins can be isolated in a pure state without any poisonous substances originating from the cell membrane, so that they will be widely available with no restriction. Secondly, even though the production of proteins would be inhibited by their own excessive formation, transfer thereof out of the biosynthetic system will free them from the feedback inhibition, which enables their excessive production. Thirdly, those proteins which deteriorates the growth of cells can be moved out of the cells which enables their production without inhibiting normal growth of the cells.
Several kinds of such signal peptides and DNA base sequences thereof have been known. For example, a signal peptide for penicillinase for Bacillus licheniformis (Nucleic Acid Research, Vol. 19, No. 11, 2577 (1981)) and a signal peptide for .alpha.-amylase for Bacillus amyloliquefaciense (Gene, 15, 43 (1981)) have been known.
The present inventors have carried out the cloning of .alpha.-amylase gene of Bacillus subtilis which has been known for its very high .alpha.-amylase productivity, analyzed the resulting cloned gene and found a novel signal peptide different from the known signal peptide and DNA base sequence thereof for amylase.
Production of proteins by the use of the DNA of the present invention in a host vector system wherein Bacillus subtilis of a high .alpha.-amylase productivity is employed as the host is superior in stability and secretion productivity to those by the use of other organisms or other signal peptides.